Direct analysis of microbial or other DNA in the environment for purposes such as environmental manipulation has been focused on in recent years. In particular, techniques for the analysis of soil microbial DNA have been researched in various ways (e.g., see Hoshino et al. “DNA Extraction from Soil” Journal of Environmental Biotechnology, Vol. 5, No. 1, pp. 43-53, 2005 (Non Patent Document 1)). However, extracting DNA from such soil microorganisms requires troublesome operations, such as centrifugation.
Researchers have also been exploring ways to detect organisms such as bacteria and viruses by trapping biological samples in a fluid such as air or a liquid that contain bacterial, viral, and other nucleic acids and analyzing the nucleic acids in the trapped biological samples (e.g., identifying and quantifying the nucleic acids) using biological techniques, such as gene analysis, for purposes such as the prevention of hospital infections, preparation for pandemics, and health improvement in developing countries. At present, however, there is no established specific method for trapping atmospheric biological samples that contain nucleic acids and analyzing the nucleic acids.
Traces of biological samples in fluid such as air, unlike those in soil, are difficult to collect in sufficient quantities using techniques such as centrifugation. This would require filtering some large amount of air in such a manner that the trapped biological samples are concentrated on the filter.
However, the use of a known and commonly employed membrane or gelatin filters, for example, causes various problems. For example, when a membrane filter is used, it is difficult to collect a biological sample entrapped inside the complicated pore structure of the membrane filter. When a gelatin filter is used, the gelatin is denatured when exposed to atmospheric water. Likewise, collecting very minor biological samples in a liquid faces the problem of the need for troublesome operations, such as centrifugation.
Under these circumstances, it is an object of the present invention to provide an extraction method and an extraction device with which the user can trap a biological sample in a fluid through filtration and efficiently extract nucleic acid alone from the trapped biological sample.